<!DOCTYPE html>
<html>
    <head>
        <style type="text/css">
            html, body {
                margin: 0;
            }
            div {
                position: absolute;
                width: 100px;
                height: 100px;
                opacity: 0.5;
                background-color: green;
            }
        </style>
    </head>
    <body>
        <div></div>
    </body>
</html>
